Remember when the Matrix turned to dust and reformed in ROFT. This means at least it has similar properties to Transformium. Or it's made of Transformium. The Matrix being the only other object that can produce Energon other than the Allspark. This leads me to think the Matrix was an attempt of the Creators to copy the Allspark. At some point it became a sacred object for Transformers. When the Allspark needed a new vessel the Matrix was a convenient replacement.